1. Field of the Invention
The present invention relates to a displacement detection device for detecting a displacement of an object by using a Hall effect element, and in particular, to a displacement detecting device suitable for application to a torque detector of an electric steering for vehicles.
2. Description of the Prior Art
Generally, in a displacement detection device using a Hall element, since the Hall element per se is temperature dependent, it is necessary to perform temperature compensation.
In order to achieve temperature compensation, in the prior art device, generally, as shown in FIG. 7a, a thermistor 51 has been inserted in the input current circuit of a Hall element 50. Alternatively, as shown in FIG. 7b, a thermistor 52 has been inserted in the voltage output side of a Hall element 50, or as shown in FIG. 7c, a constant voltage input circuit has been used.
However, in the prior art temperature compensation system of the Hall element, since the flux density of a magnet changes with a change in temperature, it is necessary to compensate for such flux density sensitivity at the same time. As a result, a compensating circuit becomes complicated and still it has been difficult to attain accurate sensitivity compensation. Moreover, another problem is involved in that it has been impossible to inclusively compensate for non-uniformities in changes in characteristics of the Hall element and the magnet due to temperature, and accurate detection of a displacement has not been achieved.
Furthermore, when a set of Hall elements are used to detect displacement based on their output voltages, if abnormalities occur in the output voltages of the Hall elements, it has been impossible to detect the abnormality.